1. Field of the Invention
The present invention relates to a high-energy ion implanter.
2. Description of the Related Art
In a semiconductor device production process, an important process is generally performed in which ions are implanted into a semiconductor wafer in a vacuum state so as to add impurities to crystals of the semiconductor wafer. Accordingly, a conductive property is changed so that the semiconductor wafer becomes a semiconductor device. An apparatus used in this process is generally called an ion implanter that accelerates impurity atoms as ions for the semiconductor device and implants impurity atoms into the semiconductor wafer.
Hitherto, an apparatus for performing a high-energy ion implantation by further deeply implanting an ion beam into the semiconductor wafer has been used with the high integration and the high performance of the semiconductor device. Such an apparatus is particularly called a high-energy ion implanter. As an example, there is known a method of configuring an ion beam acceleration system by a tandem type electrostatic accelerator.
(Batch Type)
Further, a batch treatment type high-energy ion implanter with a radio frequency linear accelerator for performing a radio frequency acceleration has been used for many years.
The batch treatment type ion implantation is a method of uniformly implanting ions into wafers while several tens of silicon wafers are loaded on the outer periphery of an aluminum disk having a diameter of about 1 m and the disk is rapidly rotated by 1000 revolutions per minute. In order to prevent the pop-out state of the wafer by a centrifugal force, the wafer loading portion of the disk has an angle of about 5° with respect to a rotation surface (a surface perpendicular to a rotation shaft). The batch treatment type ion implantation method has a problem in which an implantation angle (an angle at which the ions are incident to the wafer) is different by about 1° between the center and the end of the wafer (the implantation angle deviation) due to the above-described angle and the rotation of the wafer.
In general, a die on the wafer has anion implantation performing region and a non-ion implantation performing region, and the non-ion implantation performing region is covered by an organic substance called a photoresist. Since the ions do not need to penetrate the photoresist during the implantation, the photoresist to be coated during the high-energy ion implantation is much thickened. In the ion implantation performing region, the photoresist is excluded by lithography. However, when the integration degree is high and the implantation region is minute, the ions are perpendicularly implanted to a bottom of a deep hole surrounded by an upright photoresist wall. In the ion implantation in the structure having a high aspect ratio, the high precision of implantation angle is demanded.
In particular, in a case where a high-quality imaging device such as a CCD is produced, the resolution increases with the deep ion implantation, and hence the sensitivity is improved. For this reason, a super-high-energy ion implantation (3 to 8 MeV) is also performed. In this case, the allowed implantation angle error is about 0.1°, and a batch type apparatus with a large implantation angle deviation may not be used.
(Single Wafer Type High-Energy Ion Implanter)
Therefore, a single wafer type high-energy ion implanter has been practically realized in recent years. In the batch type, the ion beam is uniformly implanted in the horizontal direction in a manner such that the beam is fixed and the wafer moves (the rotation on the disk). On the contrary, in the single wafer type, the beam moves (so that the beam scans in the horizontal direction) and the wafer is fixed. In this type, when the scan beam is collimated, the implantation dose may be uniform within the wafer surface, and the implantation angle may be also uniform. Accordingly, the problem of the implantation angle deviation may be solved. Furthermore, the dose uniformity in the vertical direction is realized by moving the wafer at a constant velocity in both types, but the angle error does not occur in accordance with the movement.
In addition, since the single wafer type ion implanter does not uselessly consume the silicon wafer when a small number of wafers are treated, the single wafer type ion implanter is suitable for a small lot multi-product production, and hence a demand therefor has been increased in recent years.
Here, in the production of the high-quality imaging device, there is a need to meet various difficult demands in which the angle precision is needed, the metal contamination needs to be removed, the implantation damage (the residual crystal defect after the annealing) needs to be small, and the implantation depth precision (the energy precision) needs to be good. Accordingly, even the single wafer type ion implanter has many points to be improved.
In the single wafer type high-energy ion implanter of the related art, the tandem type electrostatic accelerator or the radio frequency acceleration type heavy ion linac (the linear accelerator) has been used as the high energy acceleration type.
The downstream side of the acceleration system is provided with an energy filtering magnet, a beam scanner, and a parallel (parallelization) magnet that collimates a scan orbit by a magnetic field. Then, the beam has the same incident angle (implantation angle) with respect to the wafer at any scan position due to the parallel magnet. The ion energy is up to about 3 to 4 MeV.
Further, in a part of the (single wafer type) medium current ion implanter used in the energy region (10 to 600 keV) lower than that of the high-energy ion implanter, an electric field parallel lens is used which collimates the scan orbit by the electric field (the electrode). Since the electric field parallel lens may collimate the scan orbit while keeping the symmetry of the orbit, the angle precision is more critically treated compared to the parallel magnet. Further, in this apparatus, an electric field type deflection electrode called an AEF (Angular Energy Filter) is attached to the vicinity of the wafer. Since the ions subjected to a change in charge state during the transportation of the beam or the particles generated in the beamline are removed by the AEF, a highly pure beam may be supplied.